The invention relates to polyurethane products and methods for producing them. More particularly, it relates to catalyst compositions for forming the polyurethane products.
Manufacturers of polyurethane articles require ever-improving processing technology to meet the escalating pressures of cost efficiency and complicated part design. Two important parameters affecting the ability of a manufacturer to meet these challenges are the ability to fill the mold completely and rapidly before the initiation of the polyurethane reactions increases the viscosity, and the ability of the system to cure very rapidly thereafter so that the part can be quickly removed from the mold (“demolded”). It is desirable for the polyurethane-forming composition not to react significantly or increase excessively in viscosity until it has essentially filled the mold. Delaying the polyurethane initiation time in this way provides a longer time window for filling the mold, thereby allowing the production of more complex parts, and frequently also allows for longer screw cleaning cycles. At the same time, reducing the overall reaction time increases the productivity of the expensive capital equipment used for making the parts. The total elapsed time from the beginning of injection into the mold until the part is removed is commonly referred to as “demold time”. Both initiation time and demold time can be strongly affected by the choice of type and amount of catalyst. However, catalysts that delay the onset of the polyurethane-forming reaction also frequently increase the demold time, thus increasing incremental cost.
At the same time, there is a trend toward the production of polyurethane foams having lower and lower densities, which tends to increase demold times, thereby further hurting productivity. Thus there is an increasing need for a delayed action catalyst, i.e. a catalyst that will delay the onset of reaction of the isocyanate, commonly referred to as “initiation time” or “cream time,” and still not substantially increase the demold time. Alternatively, there is also a need for a catalyst that will yield the same initiation time with a shorter demold time. Thus improved polyurethane catalyst systems are sought in the industry.